An Imidazoline–Aminophenol (IAP) Nickel Catalyst: Structure and Catalytic Activity in the Enantioselective 1,4‐Addition of 3′‐Indolyl‐3‐Oxindoles to Nitroethylene

Abstract

The structure of a nickel complex of imidazoline-aminophenol (IAP) prepared from IAP with Ni(OAc)2 was elucidated as cis-bis(imidazolineaminophenoxide) [Ni(IAP)2]. The [Ni(IAP)2] complex smoothly promoted catalytic asymmetric 1,4-addition of 3'-indolyl-3-oxindole to nitroethylene to provide chiral mixed 3,3'-bisindoles with high enantioselectivities. Mechanistic studies using ESI-MS analyses suggest that one IAP ligand dissociated from [Ni(IAP)2] to generate the Ni-enolate of 3'-indolyl-3-oxindole. From the optically active 3,3'-mixed indole adduct, biologically important 3'-indolyl-3-pyrrolidinoindoline was successfully synthesized in a three-step reaction sequence.